Making it look nice

main.js

1. import {Style, Fill, Stroke}
2. 정적 스타일 적용

const layer = new VectorLayer({
  source: source,
  style: new Style({
    fill: new Fill({
      color: 'red',
    }),
    stroke: new Stroke({
      color: 'white',
    }),
  }),
});

3. 동적 스타일 적용

• npm install colormap
• import colormap, {getArea}
• 영역크기를 기준으로 색상을 결정하는 함수 작성

import {Style, Fill, Stroke} from 'ol/style';
import Snap from 'ol/interaction/Snap';
import Draw from 'ol/interaction/Draw';
import Modify from 'ol/interaction/Modify';
import DragAndDrop from 'ol/interaction/DragAndDrop';
import GeoJSON from 'ol/format/GeoJSON';
import Map from 'ol/Map';
import VectorLayer from 'ol/layer/Vector';
import VectorSource from 'ol/source/Vector';
import View from 'ol/View';

import colormap from 'colormap';
import {getArea} from 'ol/sphere';
const min = 1e8; // the smallest area
const max = 2e13; // the biggest area
const steps = 50;
const ramp = colormap({
  colormap: 'blackbody',
  nshades: steps,
});

function clamp(value, low, high) {
  return Math.max(low, Math.min(value, high));
}

function getColor(feature) {
  const area = getArea(feature.getGeometry());
  const f = Math.pow(clamp((area - min) / (max - min), 0, 1), 1 / 2);
  const index = Math.round(f * (steps - 1));
  return ramp[index];
}

const map = new Map({
  target: 'map-container',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});

const source = new VectorSource();
const layer = new VectorLayer({
  source: source,
  style: function (feature) {
    return new Style({
      fill: new Fill({
        color: getColor(feature),
      }),
      stroke: new Stroke({
        color: 'rgba(255,255,255,0.8)',
      }),
    });
  },
});
map.addLayer(layer);

map.addInteraction(
  new DragAndDrop({
    source: source,
    formatConstructors: [GeoJSON],
  })
);

map.addInteraction(
  new Modify({
    source: source,
  })
);

map.addInteraction(
  new Draw({
    type: 'Polygon',
    source: source,
  })
);

map.addInteraction(
  new Snap({
    source: source,
  })
);

const clear = document.getElementById('clear');
clear.addEventListener('click', function () {
  source.clear();
});

const format = new GeoJSON({featureProjection: 'EPSG:3857'});
const download = document.getElementById('download');
source.on('change', function () {
  const features = source.getFeatures();
  const json = format.writeFeatures(features);
  download.href =
    'data:application/json;charset=utf-8,' + encodeURIComponent(json);
});